A stone tied to a string of length l is whirled around a vertical circle with the other end of the string at the centre. At a certain instant of time the stone is at the lowest position and has a

## Current electricity – Numerical problems

- In a potentiometer arrangement a cell of emf 1.25 V gives a balance point at 35 cm length of the wire. If the cell is replaced by another cell, the balance point shifts to 63 cm. What is the emf of the second cell?

E1= 1.25 V

l1 = 35 cm

l2 = 63 cm

E1/E2 = l1/l2

E2 = l2E1/l1

E2 = 63 x 1.25/35

E2 = 2.25 V (Ans)

**A Problem for Practice**

A storage battery of emf 8 V and internal resistance 0.5 ohm is charged by 120V dc supply